1. Field of the Invention
The present invention relates to a method of assisting sample inclination error adjustment for assisting the inclination error adjustment for the axis of a ferrule held by a clamping apparatus when analyzing the form of a leading end part of the ferrule or the like by using a microscopic interferometer apparatus (also known as “interferometric microscope apparatus”), for example.
2. Description of the Prior Art
Research and development of optical fibers used for optical communications have recently been well underway.
Known as an example of this kind of optical fibers is one comprising a core having an outer diameter of about 10 μm; and cladding layer, disposed at the outer periphery of the core, having an outer diameter of about 125 μm; whereas the optical fiber is further equipped with a ferrule, disposed at a connecting end thereof, for connecting the optical fiber to another optical fiber.
The ferrule is a cylindrical component for holding and securing one end of the optical fiber in each of a set of plugs constituting an optical connector for connecting optical fibers together. After an optical fiber is inserted and secured with an adhesive or the like to the center part of the outer diameter of a ferrule, the leading end of the ferrule is polished into a mirror surface, so that two optical fibers held by respective ferrules can be connected to each other when the leading end faces of the two ferrules are butted against each other.
While the leading end face of a ferrule has been known to be polished into a plane perpendicular to the optical axis or a plane obliquely intersecting the optical axis, attention has recently been directed to one whose leading end face is subjected to PC (physical contact) polishing so as to attain a convex spherical form such that the leading end face is elastically deformed by a pressure for butting the leading end faces of ferrules against each other.
For reducing the optical loss occurring when optical fibers are connected to each other, various high-precision specs have been defined by JIS. For the PC-polished ferrule, six μm-order specs such as dimensional errors in the radius of curvature of the leading end face and positional deviation errors between the apex of the spherical leading end face of the ferrule and the center of the core of the optical fiber (the center of the fiber outer form) have been defined.
There are cases where a microscopic interferometer apparatus is used for inspecting whether a produced ferrule conforms to the above-mentioned specs or not. The microscopic interferometer apparatus is configured such that interference fringes formed by interference between object light carrying phase information such as the surface form and refractive index distribution of a minute sample and reference light reflected by a predetermined reference plate are observed, and forms and changes of the interference fringes are measured and analyzed, so as to obtain the phase information of the sample.
When inspecting the produced ferrule by using such a microscopic interferometer apparatus, a clamping apparatus is disposed at a predetermined position in front of the reference plate of the microscopic interferometer apparatus, so as to hold the ferrule to be inspected.
Since the specs for the ferrule leading end face form are in the order of μm as mentioned above, however, the measurement thereof is required to be highly accurate, whereby a measurement accuracy suitable for the inspection is hard to attain even when the ferrule held by the clamping apparatus inclines slightly. When inspecting the above-mentioned positional deviation errors between the apex of the spherical leading end face of the ferrule and the center of the core of the optical fiber (the center of the fiber outer form) in particular, a measurement accuracy suitable for the inspection is hard to attain unless the inclination error between the normal of the reference surface of the microscopic interferometer apparatus and the ferrule axis has an angle of 10 seconds or less.
The inclination error is largely attributed to cumulative errors of plug position adjusting means, plug inclination adjusting means, and the like, whereby it is practically quite difficult for the inclination error to become an angle of 10 seconds or less in the initially set state.
Though the inclination of the clamping apparatus may be adjusted while directly measuring the inclination of the ferrule, the measurement and adjustment are quite complicated and require a high accuracy, whereby the inclination error is hard to adjust.